The billionaire business magnate had told the lower court that accusations he had plotted to bribe Indian officials to win licences to mine titanium were "absolutely untrue".

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Firtash (R) was seen as a key backer of Viktor Yanukovych during his presidency

In overturning the ruling, the Upper State Court said the final decision would be made by Justice Minister Wolfgang Brandstetter.

Mr Firtash was arrested after the latest ruling, although prosecutors said it was on a European warrant relating to allegations of links to organised crime and illegal money laundering in Spain.

Has there been any US political pressure?

Mr Firtash was first detained in 2014 in Vienna, but was released after posting a record Austrian bail of €125m (£102m).

During the lower court hearing, Mr Firtash's team raised the issue of political motive.

At the time, Mr Yanukovych had just indicated he would not sign a deal bringing Ukraine closer to the EU, despite US pressure.

The judge said there may have been a US desire to remove his ally, Mr Firtash, from the scene.

"The aim was clearly to prevent [Firtash] from undermining the political interests of the US," he wrote.

Austrian police insisted the arrest was not related to political events and the US justice department appealed.

Will the US still want to extradite Mr Firtash?

With the administration of Donald Trump coming to power, the Firtash case now falls into the realm of possible links between the new president's team and Russia.

This has already claimed one scalp - national security adviser Michael Flynn, who was fired after misleading Vice-President Mike Pence about his talks with the Russian ambassador during the presidential transition.

Mr Firtash gained much of his wealth through arrangements with Russian energy giant Gazprom.

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What were the links between ex-Trump campaign manager Paul Manafort and Mr Firtash?

His business flourished after Mr Yanukovych came to power. A key paid adviser in the president's campaign was Paul Manafort, who later became Mr Trump's election campaign adviser.

Mr Manafort and Mr Firtash were linked in a real estate project to redevelop the Drake Hotel site in Manhattan.

Mr Yanukovych's opponent, Yulia Tymoshenko, argued this was a money-laundering project to siphon huge amounts of cash out of Ukraine.

Mr Firtash denies this, telling Bloomberg that although he was initially interested in the project, he changed his mind. He said he "always had clean money" and called Ms Tymoshenko a liar.

Last August, the New York Times reported finding ledgers pledging $12.7m (£9.8m) in undisclosed cash payments from the former Russian-backed Ukrainian government to Mr Manafort between 2007 and 2012.